[Mass neonatal screening using biological testing]. / Le dépistage néonatal généralisé par des tests d'analyse biologique.

Implementation of a generalized screening program for neonatal diseases obeys precise guidelines. The disease must be severe, recognizable at an early stage, accessible to an effective treatment, detected with a non expansive and widely applicable test and it must represent an important health problem. In case of positive results, treatment or prevention shall be offered immediately and any screening program has to be regularly evaluated. There is in France since 1978 a national screening program that depends on a private association ("Association française pour le dépistage et la prévention des handicaps de l'enfant") and is supervised by the "Caisse nationale d'assurance maladie" and the "Direction Générale de la Sante". Presently, five diseases are included in the screening program: phenylketonuria, hypothyroidism, congenital adrenal hyperplasia, cystic fibrosis and sickle cell disease, the latter only in at risk newborns. Toxoplasmosis represents a particular problem because screening takes place only in children of mothers that have not been controlled during their pregnancy or in case of seroconversion. Neonatal screening of phenylketonuria and hypothyrodism is unanimously recommended. That of congenital adrenal hyperplasia is approved in most countries. The cases of sickle cell disease and cystic fibrosis are more complex because: 1) all the children that carry the mutations are not affected with a severe disease; 2) there is no curative treatment; 3) parents given information are made anxious, sometimes wrongly if the disease is mild or asymptomatic. The supporters of the screening insist on the interest of an early diagnosis which makes longer the life time of these children, the possibility for the parents to utilize prenatal screening in case of a future pregnancy, and the information given to the heterozygous carriers following a familial screening. The question is raised of the extension of neonatal screening to other diseases. This is now possible due to technical progresses such as the tandem mass spectrometry that can detect about 50 diseases in an only testing. In addition of its cost and of the difficulty to ensure an efficient organization, increasing the number of the screened diseases will raise ethical problems including how the parents will be informed of an incurable disease or a late-onset disease or an entirely asymptomatic disease. It is unanimously admitted that only mendelian diseases should be detected excluding genetic polymorphisms. Analysis of the present situation suggests the following developments: 1) to actualize the guidelines for deciding of a new neonatal screening; 2) to experiment on a local scale any new screening before its extension to the whole country; 3) to create an evaluation committee including paediatricians and epidemiologists and to evaluate on the long term the future of the children; 4) to precisely define the conditions in which the heterozygous carriers will be informed following a familial investigation; 5) to store in a resource biological centre the blood samples in order to utilize this bank for epidemiology studies.

Regulation of ANP clearance receptors by EGF in mesangial cells from NOD mice.

Mesangial cells from nonobese diabetic (NOD) mice (D-NOD) that develop diabetes at 2-4 mo express an increased density of atrial natriuretic peptide (ANP) clearance receptors [natriuretic peptide C receptor (NPR-C)] and produce less GMP in response to ANP than their nondiabetic counterparts (ND-NOD). Our purpose was to investigate how both phenotypic characteristics were regulated. Epidermal growth factor (EGF) and heparin-binding (HB)-EGF, but not platelet-derived growth factor or insulin-like growth factor I, inhibited (125)I-ANP binding to ND-NOD and D-NOD mesangial cells, particularly in the latter. NPR-C density decreased with no change in the apparent dissociation constant, and there was also a decrease in NPR-C mRNA expression. The EGF effect depended on activation of its receptor tyrosine kinase but not on that of protein kinase C, mitogen-activated protein kinases, or phosphoinositide-3 kinase. Activation of activator protein-1 (AP-1) was necessary, as shown by the inhibitory effect of curcumin and the results of the gel-shift assay. The cGMP response to physiological concentrations of ANP was greater in EGF-treated D-NOD cells. These studies suggest that EGF potentiates the ANP glomerular effects in diabetes by inhibition of its degradation by mesangial NPR-C via a mechanism involving AP-1.

Effects of angiotensin IV and angiotensin-(1-7) on basal and angiotensin II-stimulated cytosolic Ca2+ in mesangial cells.

This study analyzed the influence of two main metabolites of angiotensin II, angiotensin IV and angiotensin-(1-7), on basal and angiotensin II-dependent [Ca2+](i) in rat mesangial cells. Angiotensin IV behaved as a weak agonist. Its effects were abolished by angiotensin AT(1) receptor antagonists. Treatment with angiotensin II abolished the effect of a subsequent treatment with angiotensin IV whereas two successive angiotensin IV-dependent [Ca2+](i) peaks were obtained. Angiotensin II increased [Ca2+](i) in a Ca2+-free medium whereas angiotensin IV was inactive. Leucine-valine-valine-hemorphin 7, a hemorphin specific for the angiotensin AT(4) receptor, was devoid of any agonistic or antagonistic effect. In contrast, angiotensin-(1-7), if without influence on basal [Ca2+](i), inhibited angiotensin II- and angiotensin IV-dependent [Ca2+](i) increases. Total inhibition of the angiotensin IV effect was obtained whereas association of angiotensin-(1-7) to 8-(NN-diethylamino)-octyl-3,4,5-trimethoxybenzoate, an inhibitor of inositol phosphate-mediated Ca2+ release, was necessary to suppress the effect of angiotensin II. These results provide evidence that angiotensin II metabolites may participate in the control of [Ca2+](i) in mesangial cells at the initial stage of binding to the angiotensin AT(1) receptors.

Mechanisms mediating the renal profibrotic actions of vasoactive peptides in transgenic mice.

Transgenic mice are useful tools to investigate the mechanisms of the renal profibrotic actions of endothelin and angiotensin II. The overexpression of angiotensinogen and renin genes induces renal sclerosis independently of changes in systemic hemodynamics. The same results are observed when the endothelin-1 gene is overexpressed. Transgenic mice harboring the luciferase gene, under the control of the collagen I alpha2 chain promoter, and made hypertensive by induction of a nitric oxide (NO) deficiency have been studied. In this strain of mice, luciferase activity is an early index of renal and vascular fibrosis. Luciferase activity was increased in preglomerular arterioles and glomeruli when mice were treated with N:(omega)-nitro-L-arginine methyl ester, an inhibitor of NO synthases. Bosentan (an endothelin receptor antagonist) was as efficient as losartan (an AT1 receptor antagonist) in preventing renal fibrosis, although it did not decrease BP. In short-term experiments, angiotensin II produced an increase in luciferase activity that was entirely prevented by losartan but also by bosentan. It can be concluded that, during chronic inhibition of NO, the collagen I gene is activated, which contributes to the development of nephroangiosclerosis and glomerulosclerosis. Angiotensin II plays a major role in this fibrogenic process, and its effect is at least partly independent of systemic hemodynamics and mediated by the profibrotic action of endothelin-1.

Effects of angiotensin II and antagonists on AT(1) receptor expression in mesangial cells.

Rat mesangial cells were exposed to angiotensin II, angiotensin AT(1) receptor antagonists such as losartan, EXP 3174 and candesartan, or dexamethasone for increasing periods (1-24 h). Angiotensin AT(1A) and AT(1B) receptor mRNA were measured by reverse transcription-polymerase chain reaction (RT-PCR). Angiotensin II, losartan and EXP 3174 did not modify significantly angiotensin AT(1A) and AT(1B) receptor mRNA. Candesartan increased angiotensin AT(1B) receptor mRNA and, to a lesser extent, angiotensin AT(1A) receptor mRNA. In contrast, dexamethasone decreased mainly angiotensin AT(1B) receptor mRNA. As shown by Western blot analysis, exposure of mesangial cells to angiotensin II, losartan or EXP 3174 did not produce any change in angiotensin AT(1) receptor protein, whereas dexamethasone and candesartan exerted inhibitory effects. In conclusion, the angiotensin AT(1B) receptor subtype, the most abundantly distributed in rat mesangial cells, is inhibited by glucocorticoids. The effect of candesartan is more complex with a slight stimulation of angiotensin AT(1B) mRNA and a marked inhibition of angiotensin AT(1) receptor protein. In contrast, angiotensin II and the other angiotensin AT(1) receptor antagonists studied are inactive on angiotensin AT(1) mRNA and protein.

Angiotensin II activates collagen type I gene in the renal vasculature of transgenic mice during inhibition of nitric oxide synthesis: evidence for an endothelin-mediated mechanism.

BACKGROUND: Hypertension is frequently associated with renal vascular fibrosis. The purpose of this study was to investigate whether angiotensin II (Ang II) is involved in this fibrogenic process. METHODS AND RESULTS: Experiments were performed on transgenic mice harboring the luciferase gene under the control of the collagen I-alpha(2) chain promoter [procolalpha(2)(I)]. Hypertension was induced by chronic inhibition of NO synthesis (N(G)-nitro-L-arginine methyl ester, L-NAME). Procolalpha(2)(I) activity started to increase in the renal vasculature after 4 weeks of L-NAME treatment (P<0.01) and at 14 weeks reached 3- and 8-fold increases over control in afferent arterioles and glomeruli, respectively (P<0.001). Losartan, an AT(1) receptor antagonist, given simultaneously with L-NAME prevented the increase of procolalpha(2)(I) levels and attenuated the development of renal vascular fibrosis without normalizing systolic pressure increase. Because we found previously that endothelin mediated renal vascular fibrosis in the L-NAME model, the interaction between Ang II, endothelin, and procolalpha(2)(I) was investigated in ex vivo and short-term in vivo experiments. In both conditions, the Ang II-induced activation of procolalpha(2)(I) in renal cortex was blocked by an endothelin receptor antagonist. CONCLUSIONS: During chronic inhibition of NO, the collagen I gene becomes activated, leading to the development of renal vascular fibrosis. Ang II is a major player in this fibrogenic process, and its effect on collagen I gene is independent of systemic hemodynamics and is at least partly mediated by the profibrogenic action of endothelin.

Functional evidence for an angiotensin IV receptor in rat resistance arteries.

To distinguish between the different effects of angiotensin IV (Ang IV) on resistance artery vasoreactivity, freshly isolated rat mesenteric arteries were perfused and the changes in their diameter were recorded under various conditions. Ang IV exerted vasoconstrictor effects on both normal vessels and vessels that had been precontracted with phenylephrine or serotonin. This effect was abolished by losartan or candesartan cilexetil, two type 1 angiotensin receptor antagonists, but not by PD 123319, a type 2 angiotensin receptor antagonist. No tachyphylaxis was observed for the vasoconstrictor effect of Ang IV. N(G)-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, had no effect on Ang IV-induced vasoconstriction, whereas indomethacin, a cyclooxygenase inhibitor that was inactive by itself, influenced Ang IV-induced vasoconstriction, suggesting that Ang IV could stimulate the release of prostaglandins. Treatment of preconstricted vessels by candesartan cilexetil unraveled a vasodilator effect of Ang IV that was abolished by PD 123319, a type 2 angiotensin receptor antagonist. Unexpectedly, Ang IV still produced a vasoconstrictor effect on normal or preconstricted vessels after blockade of both type 1 and type 2 angiotensin receptors. Taken together, these results show that Ang IV influences resistance artery vasoreactivity via different mechanisms, one of which implicates a functionally active type 4 angiotensin receptor.

Genotype-phenotype relationships for the renin-angiotensin-aldosterone system in a normal population.

The renin-angiotensin-aldosterone system plays an important role in blood pressure regulation by influencing salt-water homeostasis and vascular tone. The purpose of the present study was to search for associations of single nucleotide polymorphisms on 3 major candidate genes of this system with the plasma concentrations of the corresponding renin-angiotensin-aldosterone system components considered as quantitative phenotypes. Genotyping was performed in 114 normotensive subjects for different variants of the angiotensinogen (AGT) gene (C-532T, G-6A, M235T), the angiotensin I-converting enzyme (ACE) gene [4656(CT)(2/3)], the aldosterone synthase (CYP11B2), and the type 1 angiotensin II receptor (AT1R) gene (A1166C) by hybridization with allele-specific oligonucleotides (ASO) or enzymatic digestion of polymerase chain reaction products. Plasma levels of AGT, ACE, angiotensin II (Ang II), aldosterone, and immunoreactive active renin were measured according to standard techniques. Platelet binding sites for Ang II were analyzed by the binding of radioiodinated Ang II to purified platelets. B(max) and K(D) values of the Ang II binding sites on platelets of each individual were calculated to examine a possible relationship between these parameters and the AT1R genotype. A highly significant association of the ACE 4656(CT)(2/3) variant with plasma ACE levels was observed (P<0.0001). ANOVA showed a significant effect of the AGT C-532T polymorphism on AGT plasma levels (P=0.017), but no significant effect was detectable with the other AGT polymorphisms tested, such as the G-6A or the M235T. A significant effect association was also found between the C-344T polymorphism of the CYP11B2 gene and plasma aldosterone levels, with the T allele associated with higher levels (P=0.02). No genotype effect of the AT1R A1166C polymorphism was detected either on the B(max) or the K(D) value of the Ang II receptors on platelets.

Vascular endothelin-1 gene expression and synthesis and effect on renal type I collagen synthesis and nephroangiosclerosis during nitric oxide synthase inhibition in rats.

BACKGROUND: The progression of hypertension during NO deficiency is associated with renal vascular fibrosis due to increased extracellular matrix (mainly collagen I) formation. The purpose of the present study was to investigate whether endothelin-1 (ET-1) is involved in this pathophysiological process. METHODS AND RESULTS: Treatment of rats for 4 weeks with the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) 50 mg. kg-1. d-1 increased systolic blood pressure to 159+/-12 mm Hg. In animals treated with L-NAME, histological evaluation of renal sections revealed an increased formation of extracellular matrix (Masson's trichrome), and specifically of collagens (Sirius red). A part of this fibrosis was attributed to abnormal collagen I presence, because mRNA expression of the collagen I alpha1 chain (reverse transcription-polymerase chain reaction) and procollagen I formation (radioimmunoassay) were increased 3- and 2.5-fold, respectively, in the renal resistance vessels of hypertensive animals. In subsequent experiments, we examined whether ET-1 was involved in activation of collagen I formation. mRNA expression (RNase protection assay) of preproET-1 and ET-1 content (radioimmunoassay) were 10-fold and 3-fold increased, respectively, in renal microvessels of rats treated with L-NAME. Interestingly, in these vessels, ET-1 (immunostaining) was colocalized with sudanophilic lesions. Bosentan, an ET receptor antagonist (20 mg. kg-1. d-1), coadministered with L-NAME canceled the increased mRNA expression and synthesis of collagen I and attenuated the severity of renal vascular lesions without affecting L-NAME-induced high blood pressure. CONCLUSIONS: These data demonstrate that ET-1 synthesis is increased in renal microvessels when NO production is suppressed. In this model of hypertension, ET-1 is a major activator of collagen I formation in renal resistance vessels and participates in the development of renal fibrosis without affecting systolic blood pressure.

Mesangial cells from diabetic NOD mice constitutively express increased density of atrial natriuretic peptide C receptors.

BACKGROUND: Experimental evidence shows that natriuretic peptides (NPs) play a pathophysiological role in the glomerular hemodynamic abnormalities that occur in diabetes mellitus. METHODS: In this study, the cGMP response to NPs and the different subtypes of NP receptors were examined in mesangial cells derived from a genetic model of diabetes, the nonobese diabetic (NOD) mouse. Multiple mesangial cell lines were derived from diabetic (D-NOD) and nondiabetic (ND-NOD) adult mice and were studied at different passages. RESULTS: cGMP accumulation after stimulation by atrial NP (ANP) or C-type NP (CNP) was markedly inhibited in D-NOD cells irrespective of the glucose concentration (6 or 20 mM) in the culture medium. In contrast, NP receptor density measured from [125I]-ANP saturation binding curves was 7.5 times greater in D-NOD than in ND-NOD cells. No change in KD (200 pM in both cell lines) was observed. Competitive inhibition studies showed that 4-23 C-ANP, which is specific of clearance receptors (NPR-C), displaced 90% of the maximum fraction bound, suggesting the predominance of NPR-C in both cell lines. Further identification was obtained from RNase protection assay and reverse transcription-polymerase chain reaction, which also demonstrated the higher expression of NPR-C mRNA in D-NOD cells. In contrast, NPR-A mRNA was not modified. Increased expression of NPR-C in D-NOD cells was associated with an increase of ANP internalization rate at 37 degrees C, indicating that these receptors were functional. CONCLUSIONS: These studies demonstrate that the constitutive overexpression of NPR-C in D-NOD mesangial cells is associated with a decreased response of cGMP to ANP or CNP treatment. This could be due to the lesser availability of the peptides for binding to NPR-A or NPR-B or to an inhibitory effect on NP-dependent guanylate cyclase activity via the activation of NPR-C.

Angiotensin II receptors.

This review examines the recent progress in the field of angiotensin receptors. Multiplicity of these receptors was demonstrated initially on the basis of pharmacologic differences and then confirmed by expression cloning. AT1 receptors are predominant in the adult. They are widely distributed and mediate all of the known biologic effects of angiotensin II (AngII) through a variety of signal transduction systems, including activation of phospholipases C and A2, inhibition of adenylate cyclase, opening of calcium channels, and activation of tyrosine kinases. AT2 receptors are predominant in the fetus, but also present in adult tissues such as the adrenals, ovaries, uterus, and brain. AngII via these receptors exerts effects often opposed to those mediated by the AT1 receptors. Signal transduction implicates protein tyrosine phosphatase stimulation. AT1 and AT2 receptor expressions are regulated differently, and regulation is also tissue-specific. AT1 and AT2 receptors have been demonstrated in endothelial cells. Activation of AT1 receptors results in production of vasodilatory agents, nitric oxide, and prostacyclin (PGI2), which counteract the direct vasoconstrictor effects of Ang II on the adjacent smooth muscle cells. AT1 receptors on mesangial cells, smooth muscle cells, and fibroblasts are involved in cell growth and fibrosis, the latter being due both to an increase in the synthesis and a decrease in the degradation of the main components of the extracellular matrix. These AT1 receptor-dependent effects are for the most part indirect and mediated by growth factors, cytokines, and other peptides, including endothelin, transforming growth factor-beta1, and platelet-derived growth factor. AngII is metabolized into active fragments by deletion of the terminal amino acids on both ends. AngIII and AngIV are formed by successive deletions of aspartic acid and arginine at the N terminus. AngII (1-7) is obtained by deletion of phenylalanine at the C terminus. AngIII shares the same receptors and exerts the same effects as AngII. AngIV and AngII (1-7) recognize the AT1 and AT2 receptors with a lesser affinity than AngII and, in addition, possess their own receptors that mediate effects often opposed to those of AngII.

Mesangial AT1 receptors: expression, signaling, and regulation.

Mesangial cells are one of the main targets of angiotensin II (AngII) in the renal cortex. AngII receptors on mesangial cells are of high affinity (nanomolar range). They belong to the AT1 subtype as shown by the inhibitory effect of AT1 antagonists on [125I]-Sar1, Ala8 AngII binding and on all of the biologic effects mediated by AngII, such as cytosolic calcium stimulation, inositol phosphate formation, prostaglandin production, and cell contraction. AngII also exerts long-term effects on mesangial cells, including stimulation of cell growth and synthesis of a variety of proteins, essentially the components of the extracellular matrix (collagen, fibronectin) and the type 1 inhibitor of plasminogen activator. These effects are mediated, at least in part, by autocrine products, in particular endothelin, platelet-derived growth factor, and transforming growth factor-beta, whose synthesis is enhanced by AngII. Treatment by an AT1 receptor blocker of mice with experimental nephritis inhibits activation of type I collagen alpha2 chain promoter and prevents the development of glomerulosclerosis. AngII receptors in rat mesangial cells are equally distributed between the AT1A and AT1B isoforms. Treatment of these cells by AngII or losartan, an AT1 receptor blocker, has no effect on AT1A and AT1B receptor mRNA expression, whereas candesartan, another AT1 receptor blocker, increases and dexamethasone decreases this expression.